L88 SUMMARY OF CURRENT RESEARCHES RELATING TO 



when surface-dried, if kept in very moist air. 8. Continued desiccation 

 results in the loss of the water of the sap-cavity of all mature leaf-cells, 

 recovery depending on the duration of the desiccation. 9. The rela- 

 tively xerophilous epiphytic Hymenophyllaceai owe their ability to resist 

 drought to the capacity of the protoplasmic utricle of the leaf -cells, both 

 to survive the replacing of the sap-cavity by air. and also to lose a 

 rapidly diminishing amount of water on continued desiccation. 10. The 

 Hymenophyllacese (structurally and physiologically a very distinct group 

 of' ferns) have developed forms capable of growing in relatively dry situa- 

 tions, through possession of an intercellular or functional xerophily, much 

 less pronounced than that possessed by many mosses and selaginellas, but 

 like it in kind. 



Significance of the Periplasmodium.* — E. Hannig has studied the 

 origin and development of the periplasmodium in Equisetum Umosum 

 and in Azolla. In Equisetum the tapetal cells fuse into a multinucleate 

 mass of protoplasm, and the individual cell-walls are replaced by a single 

 new membranous sheath. The vacuolar substance towards the exterior 

 of the periplasmodium gives rise to the middle lamella of each spore- 

 membrane, and also to the elater sheath, which ultimately forms the 

 elaters. The latter, which are of complex structure, arise at a definite 

 part of the spore, and extend in a spiral manner towards both poles. 

 The independent origin of the middle lamella and the elater sheath is 

 definitely proved, and the periplasmodium must be regarded as a living 

 protoplast, having a special formative and regulating function. 



In Azolla the present unisexual sporangia have been evolved from a 

 former bisexual condition. The origin of the periplasmodium is similar 

 to that in Equisetum, but the subsequent developments are more complex. 

 The periplasmodium undergoes a marked increase in volume owing to the 

 storage and assimilation of starch. The vacuolar substance gives rise to 

 the spores, of which each vacuole contains an equal number. In the 

 macrosporangium thirty-one macrospores degenerate, while one develops, 

 and under the influence of the periplasmodium the triradiate outgrowth 

 on its surface is turned towards the micropyle. Within the periplas- 

 modium, and derived from it, are the massula3, with honeycomb-like 

 walls, which eventually give rise to the swimming-body of the macro- 

 spore. The macrospore-sheath and the perispore are also derived from 

 the perisplasmodium. These results confirm those obtained with Equi- 

 setum as to the importance of the role played by the periplasmodium. 



Lepidodendron Brownii.j — R. Chodat gives an account of the 

 anatomy of a fossil stem, which he identifies as Lepidodendron Brownii, 

 and which he finds to have essentially the structure of Lepidostrobus 

 Brownii Schimp., as described by F. 0. Bower. 



Leaves of Calamites.J— H. H. Thomas gives an account of the 

 structure of the leaves of some species of the Calamocladus section of 

 Calamites. In one, which appears to be C. charseformis, the leaves are 

 very small, falcate, arranged in alternating whorls of four on slender, 



* Flora, cii. (1911) pp. 209-78 (2 pis. and 24 figs.). 



t Bull. Soc. Bot. Geneve, iii. (1911) pp. 5-6, 8-13 (7 figs.). 



X Proc, Roy. Soc, Series B, lxxxiii. (1911) pp. 490-1. 



